Slurry of manganomanganic oxide particles and method for the production of slurry

ABSTRACT

A stable non-settling slurry of water and manganomanganic oxide particles having a particle size below 10 μm. The slurry comprises water and up to 92 wt % manganomanganic oxide particles bade on the weight of the slurry. The slurry has a pH between 9 and 11 and contains 0.05 to 0.5 wt % of a dispersant based on the weight of dry manganomanganic oxide particles. The dispersant can be an ethoxylated polycarboxylate or a polyacrylic acid salt and has a molecular weight between 500 and 50 000 g/mol.

TECHNICAL FIELD

The present invention relates to a slurry of manganomanganic oxideparticles and to a method for the production of such slurries.

BACKGROUND ART

U.S. Pat. No. 5,007,480 discloses drilling mud and oil well cementslurries for different purposes such as well cementing, completionfluids, packer fluids, drilling fluids, isolation fluids and otherrelated fluids containing manganomanganic oxide particles as a weightagent. The particle size of the manganomanganic oxide particles isgenerally below 10 microns with an average particle diameter less than 1micron.

One drawback with the use of the manganomanganic oxide particlesdisclosed U.S. Pat. No. 5,007,480 is the poor flow characteristics ofthe dry particles. Both for offshore and on-shore use of themanganomanganic oxide particles, it would be convenient to use silos forhandling and storing the material. However, due to the poor flowcharacteristics of the material, it is difficult to discharge thematerial from silo-trucks, silos of delivery boats or stationary silosbecause the fine particles tend to form bridges in silos and handlingsystems, particularly in the presence of moisture.

For the same reasons, clearly, metering and feeding of the material intodrilling mud and oil well cement slurries from a silo of any size by theuse of screw conveyors or vibrating devices is inaccurate andunreliable, or sometimes even impossible.

The manganomanganic oxide particles lose their flowability afterhandling and may no longer flow freely after being stored at a site,even for a short time. This may require substantial human effort toremove material from a blocked silo, unless the silo is speciallydesigned and fully equipped with special and expensive devices to handlesticky materials. In some instances, the material may therefore also bedifficult to move over longer distances using pneumatic transportsystems, as are commonly used in the industry.

Material handled in big bags shows a similar lack of flowability, andemptying a big bag through a bottom spout might become impossible withthe result that the whole bottom of the bag might need to be cut away toget the material out.

In order to solve flowing and dusting problems of the manganomanganicparticles, it is proposed in EP 1776435 B1 to make spray dried granulesby first making a liquid slurry (containing 5-35% by weight ofmanganomanganic oxide, water and at least one water-reducing agent,and/or at least one binder agent and/or at least one dispersing agent)and spray drying the slurry to provide granules. The granules can thenlater be re-dispersed in water or oil when used for drilling muds or oilwell cement slurries. The method of EP 1776435 does however have thedisadvantages that the spray drying process requires a significantamount of energy, and that it sometimes can be difficult to re-dispersethe granules fully into individual particles.

The manganomanganic oxide particles comprise at least 90% by weight ofmanganomanganic oxide (Mn₃O₄), the reminder being calcium oxide,magnesium oxide and preferably less than 1% by weight of elementalmanganese. The density of the manganomanganic oxide particles is between4.7 and 4.9 g/cm³ and they have a particle size of at least 98% below 10μm.

DESCRIPTION OF THE INVENTION

It is an object of the present invention to provide a better solution tothe flow and dusting problems associated with the manganomanganic oxideparticles and to avoid the energy need associated with the method ofmaking spray-dried granules disclosed in EP 1776435.

The present invention thus relates to a stable non-settling slurry ofwater and manganomanganic oxide particles having a particle size below10 μm, wherein the slurry comprises water and up to 92 wt %manganomanganic oxide particles based on the weight of the slurry, andwherein: the slurry has a pH between 9 and 11 and contains 0.05 to 0.5wt % of a dispersant based on the weight of dry manganomanganic oxideparticles, selected from an ethoxylated polycarboxylate and apolyacrylic acid salt, the dispersant having a molecular weight between500 and 50 000 g/mol.

The benefits of using manganomanganic oxide in slurry form, as opposedto powder form, include:

-   -   handling a product in liquid form is easier than in a powder        form;    -   a slurry disperses more effectively in cement or drilling fluids        than a powder;    -   less shear energy is required to incorporate manganomanganic        oxide slurry into cement slurry or drilling fluids;    -   controlling the added quantities of slurry is easier than the        for powder;    -   handling of slurry is much safer than handling very fine dusty        powder material;    -   no lifting of big bags is required in the case of slurry;    -   the bulk density of the high solid load slurry (about 3.5        Ton/m³) is much higher than the bulk density of the powder        (about 1 Ton/m³) and this allows the use of lower deck space on        a drilling rig;    -   automated liquid partitioning systems may be used during the        cementing operations.

The use of manganomanganic oxide according to the invention, with itschemical and physical properties, enables a high solid load slurry to beproduced.

In particular, manganomanganic oxide has a high specific gravity of 4.8g/cm³, a small particle size with a average D50 of about 1 μm, and a lowspecific surface area in the range 1 to 4 m²/g. A weight % of 90 formanganomanganic oxide slurry is equivalent to 65 vol %, which is belowthe critical volume concentration of solid particles in dispersion.

Manganomanganic oxide fume has an isoelectric point around pH 6, i.e.,manganomanganic oxide has a zero zeta potential around pH 6. Therefore,the surface of manganomanganic oxide at pH 6 is neutral and above thatpH, the surface will have a negative charge due to the accumulation andthe ionization of the hydroxyl group on the surface of the Mn₃O₄. BelowpH 6, the surface becomes positively charged due to the accumulation ofthe hydronium ion (H₃O⁺) on the surface of the particles.

The isoelectric point of manganomanganic oxide may vary slightlydepending on the processing circumstances of the ferromanganeseproduction, such as the mode of furnace operation and the quality of theraw materials.

TABLE 1 Typical chemical composition of Mn₃O₄ fume estimated by XRFmethod Component Content in (%) wt [Mn] 69.25 [Mn₃O₄] 96.12 [Fe₂O₃] 2.75[SiO₂] 0.027 [PbO] 0.07 [ZnO] 0.1 [Al₂O₃] 0.004 [CaO] 0.007 [MgO] 0.21[K₂O] 0.005 [P₂O₅] 0.077 [As₂O₃] 0.003 [Na₂O] 0.02 [SO₃] 0.016 [CoO]0.01 [BaO] 0.002 Sp. gravity (kg/dm³) 4.82 Sp. surface (m²/g) 2.8

A typical chemical composition of Mn₃O₄ fume measured by XRF method isshown in Table 1. Mn₃O₄ fume contains to a varied extent some metaloxide impurities such as Fe₂O₃, ZnO, Al₂O₃, MgO, and SiO₂ etc. The pH ofMn₃O₄ fume varies in the range from 6 to 12, depending on the metaloxides content. Manganomanganic oxide fume exhibits a low charge densityas measured by the zeta potential compared to other metal oxides such assilica. This makes the slurrification of manganomanganic oxide mucheasier than other metal oxides. Manganomanganic oxide slurry showsbetter long term stability due to the low particle-particle interaction.

Various dispersants were tested for their effectiveness in producing astable high load manganomanganic oxide slurry. Those tested included:

-   -   1) Lignosluphonate (Borresperse Na, Ultrazine Na, Solus 5 from        Borregaard Ligno Tech), a lignin based anionic dispersant with a        wide variety of purities and molecular weights and its salt        form. In addition to the negative charge (as an anionic        dispersant), ligonsulphonate, also exhibits a branched structure        that provides steric stability;    -   2) Polyacrylate and polycarboxylate (Antiprex A, Antiprex 461        and Antiprex 62L from Ciba Specialty Chemicals), a linear        polyacrylic acid anionic type of dispersant. It exists in the        form of a sodium or ammonium salt;    -   3) Modified polycarboxylate such as polyether polycarboxylate        (Castament FS 20, Castament FS 40, Castament VP 95L, Melpers        0030, Melpers 3400, Melpers 5344, Melpers 9360 from BASF and        Geropon T36 from Rhodia);    -   4) Modified polysaccharide (modified starch ether);    -   5) Copolymer of acrylic acid and vinyl phosphonic acid        (Albritect CP30 from Rhodia)    -   6) Neutralized phosphonocarboxylic acid (Mirapol A400 from        Rhodia)    -   7) Polyoxyethylenalkyd phosphate ester (Rhodafac RA600), a        biodegradable linear alcohol ethoxylate phosphate ester.    -   8) Sulphonated naphthalene and melamine formaldehyde, commonly        known as superplastisizer in the construction industry and        widely used as dispersant in oil well cementing.

Most of these dispersants exhibit anionic character to increase theelectrostatic repulsive forces between the particles which in turnprovides a sufficient stabilization. However, out of more than 25dispersants investigated, only two of the dispersants produced a stable90 wt % slurry. These were: firstly the dispersant Antipex A from CibaChemicals, which is polyacrylic acid sodium salt with a molecular weightin the region of 3000 g/mol, and is an anionic dispersant, and thedispersant Melpers 9360 produced by BASF, which belongs to the class ofexthoxylated polycarboxylates, i.e. a modified polycarboxylic acid witha hydrophobic chain as a side chain. This second dispersant can beconsidered as a graft copolymer. The negative charge of the polymer mainchain is adsorbed on the surface of manganomanganic oxide via thecounter ion in the medium and the hydrophobic part is oriented to theaqueous phase and builds a steric barrier between the particles.

Preferably the slurry contains more than 80 wt % manganomanganic oxideparticles based on the weight of the slurry.

The content of dispersant is preferably between 0.07 and 0.15 wt % basedon the weight of the manganomanganic oxide particles.

One preferred dispersant is polyacrylic sodium salt with a molecularweight of about 3000 s/mol.

Another preferred dispersant is exthoxylated polycarboxylate with ahydrophobic chain as a side chain and a molecular weight of ca. 20000g/mol.

With regard to the pH range, the optimal pH range is from 9 to 11 andmore preferably from 9.5 to 10.5. This optimal pH range depends on thesurface chemistry of manganomanganic oxide and the amount of thecombined impurities.

For pH regulation or adjustment, any metal hydroxides, particularly thewater soluble hydroxides such as sodium hydroxide (NaOH), potassiumhydroxide (KOH) and ammonium hydroxide (NH₄OH) can be used. Preferably,sodium hydroxide is used. The pH regulator can be added as powder or asliquid.

The dispersant concentration depends on the type of dispersant, pH, thesource of manganomanganic oxide fume and the solid load of the slurry.The dispersant can be added as solid or liquid.

Manganomanganic oxide slurries with a solids loading up to 75 wt % arecommercially available, but the present invention seeks to increase thisfigure significantly. Using the present invention, it is possible toprepare slurries with a solids content from 0.01 to 92 wt %. It has beenfound that for slurries with a solids loading of <80 wt %, it isnecessary to adjust the amount of dispersant to achieve viscosity in theregion of 500 mPa·s. In accordance with the invention, a way to producestable manganomanganic oxide slurry is to adjust the viscosity by addingdispersant and/or pH by adding alkaline solution to create a rheologythat makes the slurry flowable and at the same time non-settable. Theamount of the dispersant and the pH regulator required will depend onthe slurry solid loading.

The process of producing manganomanganic oxide slurry enables theremoval of 1 to 4 wt % of coarse particles >45 μm via a wet sievingmethod. Coarse particles cause undesirable effects on both the slurrystability and the end application, particularly in completion drillingfluids. By pumping the slurry after preparation through a wet sievesystem the large particles can be removed and this will improve thestability and properties of the slurry.

The invention also extends to a method of producing a stablenon-settling aqueous slurry of manganomanganic oxide, comprising: mixingtogether manganomanganic oxide particles, water and a dispersant, themanganomanganic oxide representing up to 92 wt % of the slurry and thedispersant representing 0.05 to 0.5 wt % based on the weight of the drymanganomanganic oxide particles, and adjusting the pH of the slurry to avalue in the range 9 to 11, the dispersant being selected from anethoxylated polycarboxylate and polyacrylic acid salt, the dispersanthaving a molecular weight between 500 and 50 000 g/mol.

The manganomanganic oxide slurry is prepared by adding dispersant towater was added and mixed at low speed of ca 2000 rpm. The desiredamount of sodium hydroxide is added. Manganomanganic is the added intothe liquid medium at a low mixing rate and after adding all themanganomanganic powder a high shear mixing of ca. 10000 rpm is appliedfor 2 min.

For large scale mixing a high shear mixer equipped with rotor-stator ora tooth shear plate (impeller) is employed using the above mixing mode.

The invention also extends to products which incorporate the slurry ofthe invention, such as an oil well cement or a drilling fluid.

According to such an aspect of the invention, there is provided an oilwell cement composition, comprising cement powder, water and amanganomanganic oxide slurry according to the invention and optionallymicrosilica, a fluid loss additive, a retarder, and silica flour.

According to another aspect, there is provided a water-based drillingfluid composition, comprising water and a manganomanganic oxide slurryaccording to the invention and optionally NaHCO₃ (sodium bicarbonate),CaCO₃ (calcium carbonate), a viscosifier, a dispersant and a fluid lossadditive.

The invention also extends to methods of producing such productsincorporating the manganomanganic oxide slurry.

SHORT DESCRIPTION OF DRAWINGS

FIG. 1 shows a diagram for viscosity and pH as function of storage timefor a manganomanganic oxide slurry according to the invention,

FIG. 2 shows a diagram for viscosity versus shear rate for amanganomanganic oxide slurry according to the invention,

FIG. 3 shows dynamic rheology for a manganomanganic oxide slurryaccording to the invention, and

FIG. 4 shows dynamic rheology for another manganomanganic oxide slurryaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention may be carried into practice in various ways and will nowbe illustrated in the following specific description and Examples.

Example 1 Stability

In order to examine the stability of a slurry according to theinvention, a slurry was made up comprising water, 90 wt %manganomanganic oxide particles having the properties set out in Table1, 0.07 wt % by the weight of slurry of Antiprex A as a dispersant, andNaOH as a pH regulator in a quality sufficient to establish an initialpH of 10.5 The desired amount of dispersant and sodium hydroxide wasadded in advance prior to adding manganomanganic oxide powder.

The viscosity of the slurry and its pH were monitored over a period of 6months and the results are shown in FIG. 1. As can be seen, duringstorage for 6 months, the slurry dispersion showed good stability.

The rheological properties were measured using a MCR101 Physicarheometer from Antor Paar GmbH with Couette geometry (CC27). Thetemperature was controlled to 20° C. The flow and dynamic rheologymeasurements were recorded. The shear regime applied in this test wasramping up the shear rate from zero to 1000 s-1 and then back to zeroshear rate and repeat the same profile once more. The overlap of all thecurves (up and down) and the very small hysteresis loop as shown in FIG.2 indicate that the slurry recover its rheological properties rapidly.The dynamic curve (viscoelasticity) as shown in FIGS. 3 and 4 indicate agel network formation (G′>>G″). The magnitude of the storage (elastic)modulus G′ is depending of the number of interactions between thecomponents in the slurry and the strength of each interaction. Such weeknetwork is sufficient to keep the large particles suspended in thedispersion and avoid settling of such particles.

Example 2 Viscosity

The range of viscosities was investigated.

Rheological properties were measured using a MCR101 Physica rheometerwith parallel plate geometry (CC27). The temperature was controlled to20° C.

Flow and dynamic rheology measurements were recorded. The lowestviscosity achieved with using dispersant and pH adjustment was 300 mPa·sat shear rate of 20 s⁻¹ measured by Physica rheometer.

It is known that a low viscosity in a dispersion enhances the settlingrate of large particles.

It was observed that a viscosity in the range 300 to 1000 mPa·s at shearrate of 20 s⁻¹ is an optimal range for Mn₃O₄ slurry, to reduce thesedimentation tendency of large particles while allowing the slurry toremain flowable and pumpable. Therefore, the amount of dispersant andthe pH value was adjusted to obtain manganomanganic oxide slurry with aviscosity in the range of 300 to 1000 mPa·s at a shear rate of 20 s⁻¹.Examples of the shear viscosity as function of the shear rate of twomanganomanganic oxide slurries prepared with two different dispersantsis shown in FIG. 2.

The dynamic rheology measurement demonstrated that in a staticcondition, the slurry exhibits a weak gel structure (gel network) thathelps in suspending the heavy large particles (>45 μm) ofmanganomanganic oxide, as shown in FIGS. 3 and 4. As shown in FIG. 3, asan example, the storage (elastic) modulus (G′) of 10000 Pa is greaterthan and the loss (viscous) modulus (G″) at low strain <0.1%, meaningthat the system exhibits a gel structure that breaks at the cross overpoint at a strain of 0.46%.

Example 3 Oil Well Cement

A cement test using manganomanganic oxide slurry according to theinvention was conducted according to the API 10 standard. The followingcomposition shown in Table 2 was used to prepare cement slurry with adensity of 2.2 g/ml;

TABLE 2 Composition of oil well cement containing manganomanganic oxideslurry and powder as reference. Amount in grams Component Micromax LMicromax dry Water 145 177.9 Microblock ® slurry 124.3 124.3 Micromax L328.8 — Micromax dry — 296.0 Dispersant 18.4 18.4 Fluid loss additive34.5 34.5 Retarder 2.8 2.8 Silica flour 172.2 172.2 G-cement 493.4 493.4Total 1320 1320 Micromax L is a slurry in accordance with the invention,comprising 90 wt. % manganomanganic by the weight of slurry, 0.08 wt.-%Antiprex A by the weight of slurry and 0.25 wt. % sodium hydroxide bythe weight of slurry. Micromax dry is manganomanganic oxide, in powderform. Microblock ® slurry is a slurry of water and amorphous silicapowder produced by Elkem AS.

The following equipment was used to prepare and characterise the cementslurry:

Chandler fann 35 rheometer with thermo-cup, consistometer, equipment formeasuring fluid loss (HTHP), constant-speed warring mixer, 200-250 mlmeasuring cylinder and precision balance.

The results set out in Table 3 show that the rheological properties ofthe two cement slurries measured at 60° C. are quite similar withrelatively low plastic viscosity for the cement slurry containingmanganomanganic oxide slurry. That can be related to the excess ofdispersant in that cement slurry. The fluid loss is relatively higherfor the cement with manganomanganic oxide slurry, but that can beoptimised to the desired value by adjusting the amount of the fluid lossadditive and/or the dispersant.

TABLE 3 Viscosity and fluid loss of oil well cement measured at 60° C.Viscosity reading Micromax L Micromax dry 300 rpm 33 37 200 rpm 23 26100 rpm 14 15  6 rpm 2 2.5  3 rpm 1 2 Plastic viscosity (cp) 28.5 33Yield point (lb/ft2) 4.5 4 Fluid loss (ml) 77 50 Fee water (mm) 0 0Filter cake (mm) 42 25

Example 4 Drilling Fluid

This Example investigates the use of manganomanganic oxide slurry inwater-based drilling fluids

As shown in Table 4, a water based fluid with a density of 2.1 kg/1 wasprepared using manganomanganic oxide slurry. The mixing was achievedwithout difficulty. The rheology of the fluids before and after hotaging was quite similar, indicating good fluid stability. The fluid lossmeasured at 150° C. showed good performance. The results were alsocomparable with fluid containing manganomanganic oxide powder

TABLE 4 Composition of water based drilling fluid containingmanganomanganic oxide slurry. Total density is 2.1 g/ml. Mixing timeMixing speed Materials Amount in gram (min) (prm) Fresh water 494 NaHCO₃5 2 4000 Micromax-L 1289 5 4000 CaCO₃ medium 50 2 4000 CaCO₃ fine 25 24000 Viscosifier and 20 5 4000 fluid loss additive Dispersant 4 5 4000Fluid loss 7 5 4000 additive Micromax-L is a slurry according to theinvention having the same composition as the slurry used in Example 3.

TABLE 5 Properties of the water based drilling fluids of Table 4containing manganomanganic oxide slurry, before and after static hotageing at 150° C. for 16 hours. Total density is 2.1 g/ml. Before AfterTest Results ageing ageing TEMPERATURE/° C. ° C. 150 PERIOD STATIC Hours16 AGED RHEOLOGY: Temp/° C. 20° C. 20° C. 600 rpm 108 103 300 rpm 69 66200 rpm 54 51 100 rpm 36 34  6 rpm 13 10  3 rpm 11 8 Gels 10″ lb/100 ft²12.5 8 Gels 10′ lb/100 ft² 33 8 Plastic cP 39 37 viscosity Yield pointlb/100 ft² 30 29 FILTRAT Temperature ° C. 150 150 HTHP Fluid mL water 20Loss Filter cake mm 5 SAG TEST Supernatant mL 18 Liquid Density - g/cm³2 Top Density g/cm³ 2.15 Bottom Sag Factor 0.518

The equipment used for this test:

Chandler fann 35 rheometer with thermo-cup, equipment for measuringfluid loss (HTHP), constant-speed warring mixer, high pressure oven, hotaging cell and precision balance.

The filtration and sag tests are not important for a fresh slurry atroom temperature since the drilling fluids are always used at elevatedtemperatures. The values after hot aging are of great importance tojudge the mud performance and stability.

Table 5 shows that;

-   -   A) The water based drilling fluid formulated with        manganomanganic oxide slurry in accordance with the invention        exhibits good thermal stability. The viscosity data before and        after hot aging shows a thermal stable fluid.    -   B) The low sag and fluid loss after hot aging indicate that the        manganomanganic oxide is well dispersed in the drilling fluid.

1-14. (canceled)
 13. A stable, non-settling slurry comprising: water;manganomanganic oxide particles having a particle size below 10 μm, themanganomanganic oxide particles present in the slurry in an amount up to92 wt % based on the weight of the slurry; a dispersant in an amount of0.05 to 0.5 wt % based on the weight of dry manganomanganic oxideparticles in the slurry, the dispersant having a molecular weightbetween 500 and 50,000 g/mol and selected from an ethoxylatedpolycarboxylate and a polyacrylic acid salt; and a ph of the slurrybeing 9 to
 11. 14. The slurry of claim 13, wherein the amount of themanganomanganic particles present in the slurry is greater than 80 wt %based on the weight of the slurry.
 15. The slurry of claim 13, whereinthe amount of the dispersant is 0.07 to 0.15 wt % based on to weight ofdry manganomanganic oxide particles.
 16. The slurry of claim 13,wherein: the dispersant is a polyacrylic sodium salt having a molecularweight of about 3000 g/mol.
 17. The slurry of claim 13, wherein: thedispersant is an ethoxylated polycarboxylate; with a hydrophobic chainas a side chain.
 18. The slurry of claim 13, wherein: the ethoxylatedpolycarboxylate has a molecular weight of about 20,000 g/mol.
 19. Theslurry of claim 13, wherein: the ph of the slurry is 9.5 to 10.5. 20.The slurry of claim 1, wherein the ph of the slurry is adjusted usingsodium hydroxide.
 21. A method of producing a stable, non-settlingaqueous slurry of manganomanganic oxide, comprising: Mixingmanganomanganic oxide particles, water and a dispersant to form aslurry, wherein the manganomanganic oxide particles have a particle sizebelow 10 and are presenting an amount up to 92 wt % based on the weightof the slurry, the dispersant is present in an amount of 0.05 to 0.5 wt% based on the weight of the dry manganomanganic oxide particles presentin the slurry, the dispersant is selected from an ethoxylatedpolycarboxylate and a polyacrylic acid salt; and the dispersant has amolecular weight of 500 to 50,000 g/mol; and adjusting the ph of theslurry from 9 to
 11. 22. The method of claim 21, wherein: first,dispersant is added and mixed with the water; second, sodium hydroxideis added and mixed with the dispersant and water mixture; third, themanganomanganic oxide particles are added and mixed with the water,dispersant and sodium hydroxide mixture at a low rate of mixing; fourth,after adding all of the manganomanganic oxide particles to the water,dispersant and sodium hydroxide mixture, a high rate of shear is appliedto the water, dispersant, sodium hydroxide and manganomanganic oxideparticle mixture to form the slurry.
 23. The method of claim 21 wherein:the ph of the slurry is adjusted with sodium hydroxide.
 24. The methodof claim 21, further comprising: pumping the slurry through a sievesystem to remove coarse particles having a diameter greater than 45 μmfrom the slurry, after the slurry has been prepared.
 25. An oil wellcement composition comprising cement powder, water and the slurry ofclaim 13.